A vehicle typically includes an engine having a rotating camshaft and valves. The camshaft opens and closes the valves via a cam follower that follows a cam lobe on the rotating camshaft. The camshaft may be a sliding camshaft having an outer sliding shaft that is splined to an inner shaft. The sliding camshaft enables the cam lobe to be changed to an alternative cam lobe by sliding the outer shaft relative to the inner shaft in order to present the alternative cam lobe to the cam follower. One or more alternative cam lobes may be included on the sliding camshaft to enable engine power, efficiency, and/or other engine performance characteristics to be modified.
Both the inner and the outer surfaces of the outer shaft must be hardened for wear resistance. In addition, compressive residual stress in the outer portion of the outer shaft enables the sliding camshaft to operate under higher loading conditions, which may improve engine performance. Because the outer shaft has relatively thin walls, conventional heat treating processes result in hardening of the entire outer shaft, leaving little or no capacity for compressive residual stress in the outer portion of the outer shaft.